Coffee made in the morning and just left to sit is a common sight in many workplaces and old school diners. Anyone who’s tried it probably remembers the taste, and not in a nice way.

Common sense dictates that brewed coffee doesn’t stay good forever, but when exactly does it go bad, and why? Let’s find out.

How Long Is Brewed Coffee Good For?

To give a short answer to the question, only for 30 minutes or so, unless you store it in an airtight thermos. This is because coffee continues to oxidize even after brewing.

The freshness of your coffee will also depend on the beans you use, meaning that using stale grounds will produce a stale cup of coffee even when it is “fresh”.

Understand The Chemistry Of Coffee Oxidization

Contact with air causes roasted coffee beans to oxidize. Essentially, this is the same thing that happens to apples when you slice them open (1) and leave them for a while.

Although oxidization isn’t visible to the plain eye in the case of coffee beans, it has a significant impact on their taste. This is because oxidization causes the flavor compounds in the coffee to deteriorate and be released into the air upon contact.

When roasted coffee beans are stored properly, their oxidization process slows down, so they remain good for a few weeks.

However, once the beans are ground, they will start to oxidize more quickly (2), because their surface area increases by over 10,000 times in case of a fine espresso grind.

The process of brewing coffee itself is actually oxidization. When the coffee beans come into contact with water, they will begin releasing their aromatics, oils and acids into the water.

This chemical reaction is what produces the flavorful cup of coffee we know and love. You just want to avoid it happening before brewing. As you can see, the heat plays an important role in the flavour of hot, or cold brewed coffee: (3)

"Coffee solubles dissolve best between 195 to 205 degrees Fahrenheit, so coffee brewed with hot water has a more full-bodied, flavorful taste profile than coffee brewed with room-temperature or cold water, which is also called cold brew." - Julia Calderone, The Business Insider

Watch this video for more information on how long coffee beans stay good:

Why Does Coffee Turn Bitter?

You should know that oxidization doesn’t stop once your coffee is brewed.

When you leave your coffee to sit for too long, the reaction between hydrogen and oxygen will raise the pH level of the coffee, making it taste bitter or “stale”.

This is why you should never let your coffee sit in a brewing pot for longer than necessary.

If you can’t drink it all, place it in an airtight container like a thermos bottle.

Over-extraction is also a common cause of bitterness. To avoid it, ensure that your grind size isn’t too small and that you aren’t brewing your coffee for too long.

Even after you’ve pressed the plunger down, your coffee will continue to brew for as long as it remains in the press, turning horribly bitter in a few minutes. Pour the coffee into a mug, a serving jug or a thermos as soon as it is done.

Remember That Stale Grounds Make For Stale Coffee

The older your coffee grounds are, the more they have been subject to oxidization. Coffee made from old grounds will taste stale even immediately after brewing.

Coffee doesn’t go bad in the same way things like milk do. Old coffee grounds aren’t characterized by a rotten smell but by an absence of scent.

If that’s what you’ve been wondering about this whole time, stale coffee isn’t dangerous to drink, just unpleasant. Unless you put milk in it - in that case, you shouldn’t drink it (3) after two hours.

Ready To Enjoy Some Fresh Coffee?

If you often find yourself making more than you can drink at once, invest in a good thermos which will prolong the vitality of your coffee for a few hours. If you can, use fresh coffee beans and grind them only just before brewing.

With these tips, you’ll never have to gulp down a cup of stale coffee ever again. Enjoy!

Got any more questions about the best way to keep coffee fresh? Let me know in the comments!

Frequently Asked Questions

Can I drink day-old coffee?

We don’t recommend drinking day-old coffee, especially if it has gone rancid and has accumulated an unpleasant smell and/or taste. Brewed coffee also has a tendency to accumulate molds especially when kept outside the fridge. Do not drink day-old coffee if it has milk mixed in it, unless you kept it in the fridge.

How long can you keep brewed coffee in the fridge?

You can keep brewed coffee in the fridge for up to a week although it will not taste or smell as good as a freshly brewed cup. Just make sure to cover your cup or carafe to keep your drink from absorbing the scents and aroma of other foods or beverages inside the fridge.

How long can coffee sit out with milk?

According to the US FDA (5), perishable products like milk should not stay out of the fridge for more than two hours. The same goes for coffee that has been sitting out with milk. So if you plan to drink your coffee with milk at a later time, make sure to put it in the fridge.

References

Why do apple slices turn brown after being cut? (n.d.). Retrieved from https://www.scientificamerican.com/article/experts-why-cut-apples-turn-brown/

Alex

Alex is the Founder and Editor of Homegrounds.co. He is passionate about brewing amazing coffee at home, and teaching others to do the same.

Click Here to Leave a Comment Below 2 comments

DP - May 19, 2018

I don’t see an expiration date or a “Best Before” date on Starbucks Cold Brewed Coffee sold in grocery stores (refrigerated near dairy).

Starbucks customer service says (in email) there is a Best Before date but I don’t see it anywhere and they don’t seem to know either. I’ve had other people look, even grocery store employees who were surprised as well.

Save my name, email, and website in this browser for the next time I comment.

Alex - May 22, 2018

Yes. If you consume this coffee you will definitely die a slow, painful death.

…Im only kidding, you won’t die, but your tastebuds will hate you. I’d strongly advise against buying coffee beans from the grocery story, or from Starbucks. If there is no best before or roast date, I don’t touch it.

Buy from a local roaster, or an online coffee bean marketplace that roasts AFTER you purchase. Do a google search; there are plenty of them out there.

Your cold brew will taste SO much better if you use good quality, fresh beans.

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